Based on the true story of a family swept away by the deadly 2004 tsunami that pummeled Southeast Asia, “The Impossible” is about as subtle as a wall of water.

The depiction of the natural disaster itself, which killed 230,000 people, is visceral and horrifying. Director Juan Antonio Bayona has crafted an event that’s impeccable from a production standpoint with its dizzying, seemingly endless sprawl of destruction, a relentless, wet menace full of things that snap and stab and strangle. And Naomi Watts gives a vivid, deeply committed performance as the wife and mother of three young boys who finds the strength to persevere despite desolation and debilitating injuries.

But man, is this thing heavy-handed. Although “The Impossible” sucks you in at the start, it proceeds to pound you over the head after that.

Watts and Ewan McGregor co-star as Maria and Henry, a happily married British couple spending Christmas at a luxury resort in Thailand with their adorable sons, played by Tom Holland, Samuel Joslin and Oaklee Pendergast. (The real-life family whose story inspired the film was Spanish, like the director himself; changing their ethnicity and casting famous people to play them seems like a rather transparent attempt to appeal to a larger audience.)

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During a quiet morning by the pool, the first massive wave comes ashore, scattering the family and thousands of strangers across the devastated landscape. “The Impossible” tracks their efforts to survive, reconnect, find medical care and get the hell out of town. Maria and eldest son Lucas have managed to stick together, as have Henry and the youngest boys, Thomas and Simon. But neither group knows that the others are alive. The sense of loneliness and fear that sets in during those first quiet moments after the mayhem has settled are eerie.

Both halves of the family trudge on, though. The near-misses at an overcrowded hospital are just too agonizing to be true, and the uplifting score swells repeatedly in overpowering fashion, urging us to feel, as if we wouldn’t know how on our own. Surely, the inherent drama of this story could have stood on its own two feet.

Bayona lingers almost fetishistically on Watts’ wounds — the massive gash to the back of her right leg, the slashes beneath her left breast, the cuts over both eyes — then he martyrs her as she lingers near death. Meanwhile, the countless thousands of native people suffer in a blur — literally, they’re fleeting images glimpsed from the back of a rumbling pickup truck on a dirt road. Either that or they’re elderly, toothless saints spouting gibberish, but they never feel like real people who’ve just endured the devastation of the only home they’ve ever known.